How about starting with one seeing if the return spring will keep tension on the other, worst case you will have to adjust both, are you taking the tank & airbox off or just doing it at the bar?
This is from the '04 Z750 manual, but it should be similar......
2-14 PERIODIC MAINTENANCE
Periodic Maintenance Procedures
Throttle Control System Inspection
Throttle Grip Play Inspection •Check the throttle grip free play [A].
If the free play is incorrect, adjust the throttle cable.
Throttle Grip Free Play
Standard: 2 ∼ 3 mm (0.08 ∼ 0.12 in.)
•Check that the throttle grip moves smoothly from close to
full open, and the throttle closes quickly and completely
in all steering positions by the return spring.
If the throttle grip doesn’t return properly, check the throttle
cable routing, grip free play, and cable damage. Then
lubricate the throttle cable. •Run the engine at the idle speed, and turn the handlebar
all the way to the right and left to ensure that the idle speed
doesn’t change.
If the idle speed increases, check the throttle grip free play
and the cable routing.
If necessary, adjust the throttle cable as follows. •Loosen the locknut [A]. •Turn the adjuster until the proper amount of free play
can be obtained. •Tighten the locknut against the adjuster securely.
If the throttle grip free play can not be adjusted with the
adjuster, use the adjusters in the middle of the throttle
cables. •Loosen the locknut, and screw the adjuster at the upper
end of the accelerator cable all the way in. •Tighten the locknut against the adjuster securely. •Remove the fuel tank (see Fuel System (DFI) chapter).
•Loosen the locknuts [A], and turn the lower adjusters
until the proper amount of throttle grip free play is obtained.
•Tighten the locknuts against the adjusters securely.
If the throttle grip free play can not be adjusted with the
lower adjusters, use the adjuster at the upper end of the
cable again.
I've spent over 40 years of my life riding bikes .... the rest of it, I wasted ..
If it's got wheels or tits, it's gonna give you trouble !
HCST #2
Team Black '09 ..... R.I.P. - 2011.
Back in Black....2011.
Am wanting to take up the slack in my throttle (is a fair bit) as it is a bit of a pain in the butt...
What I was wondering is do I need to wind out both throttle cable's equally or only one?....
I'm guessing one is the return yeah?....Or is one the secondaries ....Thought I'd ask first
are you shitting me Disco
but yes your right, one is the return and one is the throttle cable.
generally i just start with the throttle till you have the right feel then tighten the return accordingly. make sure your turn your bars to the right at full lock as this will be when the cables are at the tightest. If you adjust them when they are at centre then you may find the return may not work so well at full lock
Chariot of Fury 50cc 2stroke Race bike Team Gumby in red SAM & SRT Survived
Blurr wrote:.....generally i just start with the throttle till you have the right feel then tighten the return accordingly. make sure your turn your bars to the right at full lock as this will be when the cables are at the tightest. If you adjust them when they are at centre then you may find the return may not work so well at full lock .....
Good advice that !! ALWAYS turn the bars lock-to-lock, with the engine running, after you have been fiddling with carbie cable adjustments.......
".....shut the gate on this one Maxie......it's the ducks guts !!............."
....Thought I'd ask first 
